1. Field of the Invention
The invention relates to a paper cutting system for use with printer mechanisms, and more particularly to an apparatus and method for double cutting paper in a printer to trim the final output paper to a standard length.
2. Background Information.
A number of printers print an image by repeatedly moving a sheet of paper forward and backward past a printing mechanism. For example, color thermal transfer printers typically transfer a color image from a plurality of ink sheets onto an output sheet from a roll of paper, which is then cut to size by an integral paper trimmer after the imaging process is completed. Thus, an output sheet from a roll of paper is moved forward and backward past three or four colors (cyan, yellow, magenta, and optionally black) of ink sheet as the various colored images are formed. For all known printers, this procedure requires an extra forward extension, or margin, at the leading edge of the output sheet (forward of the imaging area) in order for the paper transport mechanism to firmly and reliably hold the output sheet in close registration for each printing pass.
A problem with requiring this leading margin is that the output sheet of paper is usually of non-standard length (i.e., not 81/2.times.11 or 81/2.times.14 inches) because of the leading margin. In the past, some printers have overcome this problem, and printed standard length output sheets, by reducing the size of the printed image shorter length of paper, thus providing enough leading margin for proper operation of the paper transport mechanism.
FIG. 1a shows an output sheet 1 printed in accordance with the prior art. The image area 2 is reduced both in length and width in order to maintain the aspect ratio of the original image. The smaller image size thus results in loss of image resolution and detail. In addition, this technique requires substantial computational complexity, in extra circuitry or software or both, to reduce a full-size image to a smaller size.
It is therefore desirable to provide a standard length output sheet from such a printer without sacrificing the size of the image area. The present invention economically accomplishes this goal and permits printing a full-size image on a standard length output sheet.